The purpose of this study is to clarify the role of the immunologic mechanism as the major pathogenetic factor of dengue hemorrhagic fever and dengue shock syndrome. The approach would be based on the application of sensitive immunochemical techniques to study the kinetics of virus, antibody and virus antibody complex in the sera of patients who suffer from dengue hemorrhagic fever syndrome at different times in the courses of their infection. This study aims toward a better understanding of the physicochemical properties and antigenicity of each type of dengue viruse and possibly typespecific antibodies to those viruses. Detection of circulating virus, viral antigen, and virus antibody complex in the plasma of patients from the earliest stage and the quantitation of these various components of dengue infection in respect to time, course and severity of infection by sensitive immunochemical methods represent the major goals to be achieved in this study.